Partially revert optimization done to array equality with raw_eq

library/core/src/array/equality.rs

@@ -5,11 +5,11 @@ where
 {
     #[inline]
     fn eq(&self, other: &[B; N]) -> bool {
-        SpecArrayEq::spec_eq(self, other)
+        self[..] == other[..]
     }
     #[inline]
     fn ne(&self, other: &[B; N]) -> bool {
-        SpecArrayEq::spec_ne(self, other)
+        self[..] != other[..]
     }
 }
 
@@ -109,47 +109,3 @@ where
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Eq, const N: usize> Eq for [T; N] {}
-
-trait SpecArrayEq<Other, const N: usize>: Sized {
-    fn spec_eq(a: &[Self; N], b: &[Other; N]) -> bool;
-    fn spec_ne(a: &[Self; N], b: &[Other; N]) -> bool;
-}
-
-impl<T: PartialEq<Other>, Other, const N: usize> SpecArrayEq<Other, N> for T {
-    default fn spec_eq(a: &[Self; N], b: &[Other; N]) -> bool {
-        a[..] == b[..]
-    }
-    default fn spec_ne(a: &[Self; N], b: &[Other; N]) -> bool {
-        a[..] != b[..]
-    }
-}
-
-impl<T: PartialEq<U> + IsRawEqComparable<U>, U, const N: usize> SpecArrayEq<U, N> for T {
-    fn spec_eq(a: &[T; N], b: &[U; N]) -> bool {
-        // SAFETY: This is why `IsRawEqComparable` is an `unsafe trait`.
-        unsafe {
-            let b = &*b.as_ptr().cast::<[T; N]>();
-            crate::intrinsics::raw_eq(a, b)
-        }
-    }
-    fn spec_ne(a: &[T; N], b: &[U; N]) -> bool {
-        !Self::spec_eq(a, b)
-    }
-}
-
-/// `U` exists on here mostly because `min_specialization` didn't let me
-/// repeat the `T` type parameter in the above specialization, so instead
-/// the `T == U` constraint comes from the impls on this.
-/// # Safety
-/// - Neither `Self` nor `U` has any padding.
-/// - `Self` and `U` have the same layout.
-/// - `Self: PartialEq<U>` is byte-wise (this means no floats, among other things)
-#[rustc_specialization_trait]
-unsafe trait IsRawEqComparable<U> {}
-
-macro_rules! is_raw_comparable {
-    ($($t:ty),+) => {$(
-        unsafe impl IsRawEqComparable<$t> for $t {}
-    )+};
-}
-is_raw_comparable!(bool, char, u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize);